Datasheet

Detailed description STP4CMP
10/22 Doc ID 15770 Rev 2
5 Detailed description
The STP4CMP is a charge-pump-based 4-channel LED driver designed for RGB
illumination or LCD display backlighting, using constant current topology. Each of the 4
channels can be controlled independently. When ONx is pulled high, a constant current is
sunk into the LEDx pin when a LED is connected. This constant current is defined or
programmed by the value of the resistor at I
SETX
pin.
5.1 Enable pin (EN)
The active high enable input pin is used to shut down the whole device. When this pin is
pulled low, the device enters into shutdown mode with only 5 µA max. current consumption.
An internal pulled down of 300 kΩ is present at this pin.
5.2 LED turn-on pin (ONx)
When the EN pin is pulled high, the STP4CMP provides the flexibility to control the turning-
ON/OFF on the 4 channels independently through the 4 active high ON pins. To control the
brightness of each LED channel, it is possible to drive the selected ON pin with a PWM
signal with a frequency up to a minimum T
ON
/T
OFF
of 33 µs. An internal pull-down of 300 kΩ
is present at these pins.
5.3 Programmable output current
The LED currents at the 4 channels are programmed individually through a resistor
connected from I
set1
, I
set2
, I
set3
, I
set4
to ground. The relationship between the resistor (R
SET
)
and the LED current (I
LED
) is governed by this equation:
Equation 1
R
SET
= 16 * (1.22 / I
LED
)
5.4 Charge pump
The STP4CMP charge pump can be disabled or enabled according to the CP_sel pin.
When enabled (CP_sel is high), the charge pump provides a clamping voltage of typ 5.0 V
to ensure enough headroom to drive the LEDs. An internal pull-down of 300 kΩ is present at
this pin.
The charge pump can be disabled by pulling low the CP_sel pin, based on the V
CC
and
forward voltage of the LEDs used. This allows the connection of V
CC
directly to V
OUT
to
drive the external LEDs.
At V
CC
3.1 V, the charge pump is able to maintain regulation at 5 V when the total current
drawn from it (at V
OUT
pin) is ≤ 120 mA.
At 2.7 ≤ V
CC
< 3.1 V, in order for the charge pump to maintain regulation at 5 V, the total
current drawn from it (at V
OUT
pin) must be lowered to ≤ 40 mA.